The cost of a getpage

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The cost of a getpage
What is a good, standard, in general, all-purpose estimate for the
overhead of a getpage from a DB2 buffer? I scanned the "capacity" red book
quickly and nothing popped out!

Kevin Mulcahy
CheckFree Corp.



Terry Purcell

Re: The cost of a getpage
(in response to kmulcahy@CHECKFREE.COM)
Kevin,

The only reference I've got is 0.11 millisec on a 3090J (does not include
additional cost required for physical I/O). The reference is from one of
Michael Hannan's IDUG presentations, which he would have sourced from Akira
Shibamiya (IBM Santa Teresa Lab).

Regards
Terry Purcell
CPT Consulting

> -----Original Message-----
> From: [login to unmask email] [SMTP:[login to unmask email]
> Sent: Tuesday, 14 December 1999 12:28 pm
> To: [login to unmask email]
> Subject: The cost of a getpage
>
> What is a good, standard, in general, all-purpose estimate for the
> overhead of a getpage from a DB2 buffer? I scanned the "capacity" red
> book
> quickly and nothing popped out!
>
> Kevin Mulcahy
> CheckFree Corp.
>
>
>
>
>



Richard A Yevich

Re: The cost of a getpage
(in response to Terry Purcell)
Kevin,

It is very difficult due to the following:
1 - In a buffer pool, with VPSEQT=0, the overhead of prefetch staging for a
getpage is turned off. Could be as much as 5 to 10% of the overhead of a
getpage.
2 - In V6, if using FIFO, another 10% overhead of managing hash and control
blocks that occur with LRU, is turned off.
3 - If the page is in a hiperpool, there is a millisecond cost for bringing
back to the virtual pool.

If you are asking about the pure overhead of the issuance of the getpage and
finding a match in the buffer pool, as I recall, and it has been awhile, was
about 0.1 milliseconds. However, I do not recall exactly what that took
into account.

Richard Yevich
+=====+======+
Information Technology Consulting, Data Modeling, Advanced Education
RYC® Inc. USA: 1-800-664-2421 Int'l: 1-305-361-8585 Fax: 1-512-476-3930
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Authors of "DB2 Answers" by Osborne-McGraw Hill, May, 1999


> -----Original Message-----
> From: DB2 Data Base Discussion List [mailto:[login to unmask email]On Behalf Of
> [login to unmask email]
> Sent: Monday, December 13, 1999 7:28 PM
> To: [login to unmask email]
> Subject: The cost of a getpage
>
>
> What is a good, standard, in general, all-purpose estimate for the
> overhead of a getpage from a DB2 buffer? I scanned the
> "capacity" red book
> quickly and nothing popped out!
>
> Kevin Mulcahy
> CheckFree Corp.
>
>
> To change your subscription options or to cancel your
> subscription visit the DB2-L webpage at
> http://www.ryci.com/db2-l. The owners of the list can be reached
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>



Venkat (PCA) Pillay

Re: The cost of a getpage
(in response to Richard A Yevich)
Additionally:-

Cost of getpage varies with situation. Tim Lenahan's presentation last IDUG
has excellent estimation -

Basic fetch in program - 3500 Instructions
Each contiguous columns - 90 instructions
Each non contiguous columns - 120 instructions
Stage 1 - 500 instructions
Stage 2 - 900 instructions
Row not qualifying stage 1 - 200 instructions


Prefetch I/O and data transfer cost is charged to DBM1 address space. But
for Sync I/O, the cost is to the application.
I am estimating 9000-10000 instructions for sync I/O ( This is just my
estimation and I could be wrong).

Regards
Venkat Pillay

> -----Original Message-----
> From: Purcell, Terry [SMTP:[login to unmask email]
> Sent: Monday, December 13, 1999 11:17 PM
> To: [login to unmask email]
> Subject: Re: The cost of a getpage
>
> Kevin,
>
> The only reference I've got is 0.11 millisec on a 3090J (does not include
> additional cost required for physical I/O). The reference is from one of
> Michael Hannan's IDUG presentations, which he would have sourced from
> Akira
> Shibamiya (IBM Santa Teresa Lab).
>
> Regards
> Terry Purcell
> CPT Consulting
>
> > -----Original Message-----
> > From: [login to unmask email] [SMTP:[login to unmask email]
> > Sent: Tuesday, 14 December 1999 12:28 pm
> > To: [login to unmask email]
> > Subject: The cost of a getpage
> >
> > What is a good, standard, in general, all-purpose estimate for the
> > overhead of a getpage from a DB2 buffer? I scanned the "capacity" red
> > book
> > quickly and nothing popped out!
> >
> > Kevin Mulcahy
> > CheckFree Corp.
> >
> >
> >
> > the DB2-L webpage at http://www.ryci.com/db2-l. The owners of the list
> can
> >
>
>
>
>
>